Constructing robust heterointerfaces for carrier viaduct via interfacial molecular bridges enables efficient and stable inverted perovskite solar cells

Abstract

A robust perovskite–substrate interface is critical to realize state-of-the-art inverted (p–i–n) perovskite solar cells (PSCs), as it enables charge carrier selectivity by means of suitable electrostatics, energy level alignment, and low interfacial recombination. To achieve this goal of carrier selectivity in p–i–n type PSCs, we propose a strategy of carrier viaduct via an interfacial molecular bridge comprised of Ph-CH₂N⁺H_3−n(CH₃)_n ammonium cations (where n is the degree of substitution). Through a joint theoretical–experimental study, we demonstrate that the most stable heterointerface is established by quaternary ammonium (QA, n = 3), where the –N⁺(CH₃)₃ groups preferentially insert into the perovskite frameworks, with a vertical downward orientation of the phenyl groups towards the perovskite-substrates. This interfacial molecular bridge configuration as a carrier viaduct enables directional carrier management and redistributes a homogeneous environment at the heterointerface. Therefore, the carrier viaduct strategy enhances charge carrier extraction and transport in both in-plane or out-of-plane directions. Meanwhile, the bottom interfacial molecule acts as a double-sided molecular binder, maintaining the contact stack and strengthening the weak interface. The fabricated lab-scale inverted PSCs exhibit a champion efficiency of 25.45% (certified at 24.9%), with the fill factor exceeding 85.66%, corresponding to 95% of their thermodynamic limit at its bandgap (E_g = 1.54 eV). The corresponding perovskite solar modules for an active area of 23.25 cm² deliver an efficiency of 20.91%. Notably, even unencapsulated target PSCs retain nearly their initial efficiency after 3000 hours under light soaking at maximum power point tracking.